Progressing cavity apparatus include progressing cavity motors and progressing cavity pumps.
A progressing cavity motor is frequently used to drive a drill bit in borehole drilling operations, such as operations to drill an oil and/or gas well. A progressing cavity motor receives energy from a fluid passing through the motor and converts the fluid energy to rotational energy of the drill bit.
A progressing cavity pump is frequently used to pump fluids from a borehole, such as a producing well. A progressing cavity pump receives rotational energy from a motor which is typically located at the surface of the borehole and transfers the rotational energy to a fluid which has accumulated in the pump and/or the borehole, so that the fluid energy conveys the fluid to the surface of the borehole.
Progressing cavity apparatus, including progressing cavity motors and progressing cavity pumps, are often referred to as “Moineau” apparatus, in recognition of their inventor, Rene Moineau, who obtained U.S. Pat. No. 1,892,217 for a “Gear Mechanism” on Dec. 27, 1932.
Progressing cavity apparatus are characterized by a stator and a rotor, wherein the rotor is disposed within the stator and rotates within the stator.
The stator has a helical lobed stator profile on an inner surface of the stator and the rotor has a helical lobed rotor profile on an outer surface of the rotor. Each lobe defines a separate helix or thread which winds along the length of the stator or rotor. The stator has one more lobe than the rotor. The respective pitches (i.e., the longitudinal distance required for a lobe to wind one full turn around the length of the stator or rotor) of the lobes on the stator and rotor are in the same ratio as the number of lobes on the stator and the rotor respectively. For example, if the stator has three lobes, the rotor will have two lobes and the ratio of the pitch of the lobes on the stator to the pitch of the lobes on the rotor will be 3:2.
Another feature of progressing cavity apparatus is that each lobe of the rotor is constantly in contact with the stator at any transverse cross section. This has the effect of creating a plurality of empty spaces between the stator and the rotor which each have a length equal to the pitch of the stator. The number of empty spaces is equal to the number of lobes on the stator. The empty spaces are isolated from each other by the points of contact between the rotor and the stator, which are often referred to as “seal lines”.
The empty spaces between the stator and the rotor may be repeated in “stages” along the length of the progressing cavity apparatus, wherein a stage is defined by one full rotation of the stator lobes. As a result, a progressing cavity apparatus which includes a stator having a length equal to two times the pitch of the stator lobes is described as a two-stage progressing cavity apparatus.
As the rotor rotates within the stator, the empty spaces “move” or progress with a helical motion along the length of the apparatus. In the operation of a progressing cavity motor, these empty spaces are filled with a drive fluid which causes the rotor to rotate relative to the stator as the empty spaces move from one end of the stator to the other end of the stator. In the operation of a progressing cavity pump, these empty spaces are filled with a driven fluid which is caused to move from one end of the stator to the other end of the stator as the rotor rotates relative to the stator.
Due to the shape and geometry of the stator and the rotor, the rotor will move laterally or precess relative to the stator as the rotor rotates within the stator. In other words, the rotor moves eccentrically relative to the stator in addition to rotating within the stator.
The performance characteristics of a progressing cavity apparatus are dependent upon design parameters such as the diameters of the stator and the rotor, the number of lobes on the stator and the rotor, the pitch of the stator and the rotor, the amount of eccentricity between the stator and the rotor, and the overall length or number of stages of the apparatus.
For example, increasing the number of stages of a progressing cavity apparatus generally increases the torque capacity/pressure capacity of the apparatus and increasing the number of lobes on the stator and the rotor generally increases the volumetric capacity of a progressing cavity apparatus as well as the torque capacity/pressure capacity of the apparatus.
The performance characteristics of a progressing cavity apparatus are also dependent upon the ability of the apparatus to provide an effective seal between the rotor and the stator along the seal lines.
For example, the torque capacity/pressure capacity of a progressing cavity apparatus is proportional to the differential pressure which can be developed between the ends of the apparatus, which in turn is dependent upon the effectiveness of the seal between the rotor and the stator along the seal lines.
In order to accommodate the complex movement of the rotor relative to the stator while maintaining effective sealing along the seal lines between the rotor and the stator, stators are typically of a composite construction which includes a metal stator tube having a lining of an elastomeric material applied to an inner surface of the stator tube.
In a conventional progressing cavity apparatus, the stator tube is comprised of a cylindrical tubular member having a cylindrical tube profile on its inner surface, so that the helical lobed stator profile is provided solely by the elastomeric material. As a result, the thickness of the elastomeric lining varies considerably along the transverse cross-section of the stator. Where the elastomeric material defines a lobe it is relatively thick and where the elastomeric material defines a space between lobes it is relatively thin.
The torque capacity/pressure capacity and overall integrity of a progressing cavity apparatus is limited by the strength and durability of the elastomeric lining. The lining must be rigid enough to resist the pressure differential between adjacent empty spaces, must be flexible enough to accommodate the complex relative movement of the rotor and the stator, and must be able to withstand high temperatures, temperature fluctuations, repeated cycles of deformation, and the wearing effects of solids which may be contained in the fluid which passes through the apparatus. The lining must also resist the effects of physical and chemical interactions with substances which may come into contact with the lining.
Although the conventional progressing cavity apparatus is relatively effective, it has been found that the elastomeric lining provides a general weak link in the performance, reliability and durability of conventional progressing cavity apparatus. For example, elastomeric materials tend to exhibit a significantly higher heat capacity than metals, with the result that elastomeric linings tend to absorb and retain significant amounts of heat during operation of the apparatus, particularly in the areas where the elastomeric lining defines lobes and is therefore relatively thicker. Elastomeric materials are also prone to swelling due to heat or interactions with substances which come into contact with them, which swelling becomes more pronounced as the thickness of the elastomeric lining increases.
As a result, efforts have been made to improve the materials which are used to provide the elastomeric lining. Efforts have also been made to improve upon the conventional stator configuration in order to minimize the limitations of the elastomeric lining.
These latter efforts have resulted in the development of “high performance” progressing cavity apparatus.
In a high performance progressing cavity apparatus, the inner surface of the stator tube has a helical lobed tube profile. Depending upon how the stator tube is fabricated, the outer surface of the stator tube may be generally cylindrical or may have a helical lobed profile which substantially matches the helical lobed tube profile on the inner surface of the stator tube.
A relatively thin and substantially constant thickness of an elastomeric material is typically applied to the inner surface of the stator tube (i.e., the helical lobed tube profile) as a lining. Where the outer surface of the stator tube has a helical lobed profile which substantially matches the helical lobed tube profile on the inner surface of the stator tube, the stator tube itself may also have a substantially constant thickness.
It has been found that high performance progressing cavity apparatus can provide superior torque capacity/pressure capacity and improved reliability and durability in comparison with conventional progressing cavity apparatus.
For example, the relatively thin and substantially constant thickness of the elastomeric lining which is made possible by providing the helical lobed tube profile on the inner surface of the stator tube facilitates an improved seal between the rotor and the stator. In addition, the reduced thickness of the elastomeric lining has been found to provide superior heat dissipation and less swelling due to physical and/or chemical interactions with substances which may be contained in fluids which pass through the apparatus.
The prior art contains descriptions of high performance progressing cavity apparatus and descriptions of methods for fabricating stators for high performance progressing cavity apparatus.
U.S. Pat. No. 5,145,342 (Gruber) describes several designs for a stator, each of which purports to include a uniform layer thickness of a rubber-elastic insert material. In one embodiment, the stator tube has a helical lobed profile on both its inner and outer surfaces. In a second embodiment, the stator tube has a cylindrical profile on both its inner and outer surfaces, but metal wires are embedded in the rubber-elastic insert material along the lobes in order to maintain the uniform layer thickness of the rubber-elastic insert material. The stator tube is described as being manufactured in a known manner.
U.S. Pat. No. 5,145,343 (Belcher) describes a progressing cavity pump in which the stator is provided with a substantially constant wall thickness of an elastomeric lining.
U.S. Pat. No. 5,171,138 (Forrest) describes a composite stator for a progressing cavity motor which includes a housing, a rigid metal stator former secured within the housing and having a multi-lobed helical inner surface and a uniform thickness wall, and an elastomeric material having a substantially uniform thickness applied to the helical inner surface of the stator former. The space between the stator former and the housing may be filled with additional elastomer or with resin in order to support the stator former within the housing.
U.S. Pat. No. 6,158,988 (Jager), U.S. Pat. No. 6,162,032 (Jager), U.S. Pat. No. 6,427,787 (Jager) and Canadian Patent Application No. 2,271,647 (Jager) all describe progressing cavity apparatus which include a lining of an elastomeric material with an essentially uniform thickness and a stator tube with a helical lobed profile on both its inner surface and outer surface so that it also has a substantially uniform thickness.
U.S. Pat. No. 6,293,358 (Jager) describes a progressing cavity apparatus which includes an outer tubular member, a replaceable thin-walled inner tubular member extending within the outer tubular member and supported by the outer tubular member, and a liner attached to the inner wall of the inner tubular member. The thin-walled inner tubular member has a helical lobed profile on both its inner surface and outer surface and is described as being produced from thin walled cylindrical pipes using a permanent deformation process according to known methods.
U.S. Pat. No. 6,309,195 (Bottos et al), U.S. Pat. No. 6,568,076 (Bottos et al) and Canadian Patent No. 2,333,948 (Bottos et al) all describe a stator for a progressing cavity apparatus which includes a thick walled stator tube having a helical lobed profile on its inner profile and a matching helical lobed profile on its outer profile, and a constant thickness of an elastomer layer molded or attached to the inner profile of the stator tube. It is described that the constant thickness of the elastomer layer results in less heat generation and less swelling in aggressive drilling fluids and at higher temperatures. It is further described that the matching inner profile and inner profile of the stator tube results in the stator tube always being proximate to the sealing surface, thus reinforcing the elastomer layer and facilitating a substantial dissipation of heat due to the superior heat conducting properties of metal in comparison with the elastomer material. Furthermore, because the stator is thick walled, it is not necessary to provide a separate supporting housing for the stator tube.
U.S. Pat. No. 6,309,195 (Bottos et al), U.S. Pat. No. 6,568,076 (Bottos et al) and Canadian Patent No. 2,333,948 (Bottos et al) also describe three manufacturing methods for the stator tube. A first manufacturing method is a rolling method in which a cylinder or tube is rolled over a metal core having a helical lobed profile. A second manufacturing method is a cold drawing method in which a swaged metal tube is pulled through a pair of rotatable dies which form the helical lobed profile on the inner surface and the outer surface of the stator tube. A third manufacturing method is a hot extrusion method in which a hot metal cylinder is forced through a pair of dies, each having a helical lobed shape.
U.S. Pat. No. 6,543,132 (Krueger et al) and Canadian Patent No. 2,315,043 (Krueger et al) both describe a number of manufacturing methods for producing stator tubes for a progressing cavity motor which have a helical lobed profile on their inner surface and a cylindrical profile on their outer surface. In a first manufacturing method, a mandrel having a helical lobed profile is disposed within a metal tubular member and the tubular member is placed between at least two rollers which rotate in opposite directions, thereby moving the tubular member in the same direction. The rollers rotate back and forth, thereby providing a stroking motion to the tubular member. The method is continued until the inner surface of the tubular member attains the helical lobed profile of the mandrel. In a second manufacturing method, the stator tube is formed by compressing a tubular member by a plurality of continuously rolling rollers until the inner surface of the tubular member attains the helical lobed profile of a mandrel which has been placed inside the tubular member. In a third manufacturing method, a tubular member having therein a mandrel with a helical lobed profile is alternately pressed with a plurality of dies disposed around the outer surface of the tubular member until the inner surface of the tubular member attains the helical lobed profile of the mandrel. In a fourth manufacturing method, metal is sprayed to a desired thickness onto a frangible mandrel having a helical lobed profile, following which the mandrel is removed from the tubular member.
U.S. Pat. No. 6,604,921 (Plop et al) and U.S. Pat. No. 6,604,922 (Hache) both describe a stator tube for a progressing cavity motor which has a helical lobed profile on its inner surface and a cylindrical profile on its outer surface. A liner formed from a material such as an elastomer is applied to the inner surface of the stator tube, which liner has an “optimized” variable thickness. It is described that the helical lobed profile of the stator tube may be shaped by any means known in the art including machining, extrusion and the like.
U.S. Pat. No. 6,666,668 (Kaechele), U.S. Pat. No. 6,716,008 (Kachele) and Canadian Patent Application No. 2,387,833 (Kachele) all describe a stator for a progressing cavity apparatus which include a stator tube with a helical lobed profile on its inner surface and its outer surface, thereby providing a constant wall thickness of the stator tube, and a lining applied to the inner surface of the stator tube, which lining also has a constant wall thickness.
U.S. Pat. No. 6,872,061 (Lemay et al) describes a method for making a stator for a progressing cavity pump, wherein the stator tube is a rigid-walled metal tube having a helical lobed profile on both its inner surface and its outer surface. The shape of the stator tube is formed by subjecting metal tube to a preliminary mechanical-forming step to preform a rough shape followed by a definitive-forming step during which the rough shape is subjected to a hydroforming process. The formed stator tube is then mounted within an outer casing which forms a housing for the stator tube.
Canadian Patent Application No. 2,409,054 (Kaiser et al) and Canadian Patent Application No. 2,412,209 (Kaiser et al) both describe a hydroforming process for forming a stator tube for a progressing cavity apparatus in which a tube is placed in a hydroforming fixture and then subjected to a hydroforming process to produce a stator tube which has a helical lobed profile on both its inner surface and its outer surface. These patent applications contemplate a thin walled embodiment of a stator tube in which the stator tube is mounted inside a support housing and a thick walled embodiment in which the support housing is omitted.
Electroforming is effectively a variation of a conventional electroplating process. Both electroplating and electroforming involve electrodeposition of metal onto a cathode in an electrolytic cell. However, while electroplating typically results in the electrodeposition of relatively thin coatings on a supporting object, electroforming can result in the electrodeposition of much thicker coatings which can exist as a self supporting structure. As a result, electroforming may be used for the production of metal parts which must exhibit structural strength and integrity.
In electroforming, a conductive mandrel having a desired mandrel profile on its outer surface is first provided as a cathode in a suitable electrolytic cell. Metal is electrodeposited onto the outer surface of the mandrel to a desired thickness and then the mandrel is separated from the deposited metal, leaving a metal “shell” which has a profile on its inner surface which matches the mandrel profile.
For some mandrel profiles, the mandrel may be separated from the deposited metal simply by extracting the mandrel from the deposited metal shell. For other mandrel profiles which do not permit extraction of the mandrel, the mandrel may be separated from the deposited metal by melting the mandrel, by dissolving the mandrel, or by otherwise destroying the mandrel.
Electroforming enables the production of metal pieces having complex internal shapes which may otherwise be difficult to manufacture. Electroformed metal exhibits superior material properties, since electroformed metal is deposited in layers with a fully developed fine grained structure. Finally, electroforming is very precise and can therefore reproduce the mandrel profile virtually exactly, without the shrinkage and distortion which may be associated with other metal forming techniques, such as casting, stamping, rolling, drawing, extruding etc.
Because electroforming is effectively an electroplating process, the selection of the metal to be deposited and the components of the electrolytic cell (including the electrodes, the power supply, and the temperature and composition of the electrolytic bath) may be made in a similar manner as in a conventional electroplating process.
U.S. Pat. No. 4,461,678 (Matthews et al) describes the manufacture of a jet pump using an electroforming process, in which the electroforming mandrel consists of a mandrel assembly including a plurality of interconnected forming mandrels, which forming mandrels may be disconnected from each other in order to separate the mandrel assembly from the electrodeposited metal shell which results from the electroforming process.
U.S. Pat. No. 6,409,902 (Yang et al) describes a rapid tooling process which integrates solid freeform fabrication (SFF) with electroforming to produce metal tools including molds, dies, and electrical discharge machining (EDM) electrodes. Solid freeform fabrication is first used to produce a rapid prototyping master and a conforming anode. Electroforming is then used to electrodeposit a layer of metal onto the rapid prototyping master to form a cathode shell on the rapid prototyping master. Finally, the rapid prototyping master is removed from the cathode shell.
The prior art described above does not describe, suggest or contemplate the use of electroforming for the manufacture of stator tubes for use in progressing cavity apparatus.